Recovery of uranium from low grade uranium bearing ores



June 9, 1959 H. B. RHODES ETAL 2,890, 9

RECOVERY OF URANIUM FROM LOW GRADE URANIUM BEARING ORES Filed June 6, 1956 2 Sheets-Sheet 1 MI IE sIzE REDUCTION STEAM 0R LIGHT GASES TO COMBUSTION COMBUSTI N GASES 9 SEPARATION 2 OF REToRT RETORT PRODUCTS B cl MAKE-UP C|2+O2 CHLORINA- 'CHLORINE Clz-Oz O v T Q TION RECYCLE SEPARATION v 2 OXIDATION I l METAL oxIDEs agg sE I /A R'XT I N KCI SEPARATION WITH MOLTEN soc-650C ALKALI CHLORIDE A i cI ,si,sAND SHALE Tl CHLORINES FefilO RESIDUE COND4\ENSE ALUMINUM DIscARDED A c fiE Lw AND F SEPARATION v PoRIzE 3 WITH F6203 I I u PRODUCT Al 2 INVENTO "ZWRISDIII 5. 6 110355 R5 {UKLMM l t-sol. BY ncK M fl/ks/lazv H. B. RHODES ET AL June 9, 1959 RECOVERY OF URANIUM FROM LOW GRADE URANIUM BEARING ORES Filed June 6, 1956 2 Sheets-Sheet 2 GAS STREAM (N ,Cl ,C0C|

CHLORINATION VAPORIZAT ION CHAMBER MOLTEN BATH CONTAINER INVENTOR Al i 6. 3/0965 F/QfjOLD Uni d tates Patent 2,890,099 RECOVERY OF URANIUM FROM LOW GRADE URANIUM BEARING ORES Harrison B. Rhodes, Bnifalo, N.Y., William F. Pesold, Wyandotte, Mich., and Jack M. Hirshon, Doylestown, Pa., assignors to the United States of America as represented by the United States Atomic Energy 'Com mission Application June 6, 1956, Serial No. 589,832 17 Claims. (Cl. 2314.5)

This invention is concerned with the recovery of uranium from low grade geologic deposits. In particular the invention relates to a method of separating uranium from a gaseous chloride stream comprising major amounts of volatilized iron and aluminum chlorides and minor amounts of other volatilized metal chlorides including uranium chlorides.

The present invention is particularly adapted to separating uranium from Chattanooga shale, a mineral occurring in the State of Tennessee and bordering States. Chattanooga shale comprises an organic fraction; and a metal bearing fraction comprising about 16% by weight of the total shale. A typical composition of the shale is as follows:

TABLEI Component Weight percent SiO 55.4 0 (total) 14.1 A1 0 9.5 S (total) 5.1 Fe 4.3 K 0 3.6 Ca (as phosphate) 2.5 MgO 1.7 H 1.7 Moisture 1.0 TiO 0.6 Na O 0.4 Mo .02 V .03 Misc. 0.04 U 0.0065 The iron exists in the shale primarily in the form of pyrites.

It has been estimated that the Chattanooga shale deposits comprise the largest known uranium reserve in the world. However, the uranium exists in such small quantities (.006 to .008% of the total shale) that it has heretofore been considered impractical to recover it from the shale. The enormity of the problem may be appreciated when it is observed that the tailings from the Colorado Plateau, that is, the discard portions contain about .01 to about .05 uranium. The problem may be more graphically illustrated when it is realized that in order to recover one pound of uranium about 8 tons of Chattanooga shale have to be processed, assuming 100% uranium recovery with the uranium present as .006% of the total.

It is an object of the present invention to recover uranium from a uranium-bearing ore containing a high ratio of iron and aluminum as compared to the amount of uranium. A principal object of the invention is to provide a method for separating uranium from a gaseous stream containing major amounts of volatilized compounds of iron and aluminum and minor amounts of other volatilized metal compounds including uranium. Another important object of the "invention is to provide a method for recovering and separating uranium from Chattanooga shale. Another object of the invention is to provide a method for recovering metals contained in Chattanooga shale, other than uranium," in a commercially usable form. Still another object of the invention is to provide a method of recovering and separating uranium from a mixture of ferric, aluminum and uranium chlorides.

As applied to Chattanooga shale, these and other objects of the invention are attained by heating the shale to a temperature in the range 450 to 800 C. to remove the volatile organic components of the shale, reacting a chlorinating agent with the remaining inorganic components of the shale at a temperature in the range 600 to 1000 C. to convert the uranium to a vaporized chloride thereof whereby other metal components of the shale are also volatilized, passing the thus formed vaporized chlorides in intimate contact with a molten alkali metal chloride to quantitatively deposit uranium therein, and thereafter separating the uranium from the alkali metal chloride. We have found that an agent selected from the group consisting of phosgene, carbon tetrachloride, chlorine and a mixture of chlorine and sulfur chloride is effective to chlorinate and remove the uranium from the shale.

An important aspect of the present invention is the concentration of uranium from a mixture of aluminum, iron and uranium, wherein the ratio of aluminum and/ or iron to uranium is high by chlorinating the mixture and heating the chlorides to form a volatilized chloride stream, bringing said volatilized stream into contact with a molten alkali chloride at a temperature in the range 700 to 1000 C. to quantitatively deposit the uranium in the molten chloride and thereafter separating the uranium from the alkali metal chloride.

For purposes of discussion and illustration we shall describe the process of our invention in connection with the problem of separating uranium from Chattanooga shale. However, our method is equally applicable in situations where it is desired to separate uranium from other ores or ore residues containing relatively large quantities of iron and aluminum as compared to the amount of uranium present.

The invention will be particularly described with reference to the accompanying drawings in which Figure 1 is a flow sheet which illustrates the sequence of steps in recovering the uranium from Chattanooga shale and Figure 2 is a cross-sectional view of an apparatus suitable for use in extracting uranium from a volatilized chloride stream into a molten alkali metal.

Referring to the flow sheet a charge of shale as received from the mine is dry ground such as by crushers and rod mill to a particle size in the range 4 to +325 mesh; In most cases the shale was found to contain .006 to .008% uranium. The ground shale is then heated in a retort with steam and/or recycled combustion gases at a temperature of 450 to 800 C. to remove the volatile organic components of the shale. The object of heating the shale is to remove all organic matter volatilizable at the retorting temperature. Gases resulting therefrom may be recycled to the retort to maintain the desired temperature. We have found that the retorted shale undergoes a loss in weight ranging from 7% in some cases to as high as 25% of the total weight of the shale charge. The retorted shale at this stage contains as low as .1% to 13% carbon based on the total weight of the shale.

We have found that the shale may be heated under retorting or roasting conditions in order to remove volatile matter. Retorting may be carried out in a gas combustion retort or steam retort; roasting may be carried out in apparatus such as a Dorr type fluo-solids roaster. In either case, however, the shale should be heated in a manner so as to avoid sintering of the inorganic constituents of the shale. We have found that recovery of metal values from the shale is considerably reduced when the shale has been sintered.

The heated shale is then reacted with a chlorinating agent at temperatures in the range 600 to 1000 C. to chlorinate the inorganic portion of the shale. We have found that carbon tetrachloride, phosgene and chlorine and mixtures of chlorine and sulfur chloride are all suitable reagents for chlorinating the shale. However, since nearly all of the metals present are chlorinated to some degree under these conditions, there is an extremely high consumption of the chlorinating agent. Were the chlorinating agent not recoverable, it would add markedly to the cost of producing the uranium. In these circumstances We have found that chlorine or a mixture of chlorine and sulfur monochloride is the most elfective chlorinating agent to use when the shale has been heated without roasting. For roasted shale, any of the chlorinating agents referred to above is satisfactory. Chlorine is particularly advantageous in either case since it is easily recovered and recycled as will be hereinafter described.

In chlorinating the shale experimentally, we used a Vycor glass reactor tube charged with to 28 mesh retorted shale. The reactor tube was enclosed by a tubular furnace which provided the desired heating. A mixture of dry nitrogen and chlorine was passed through the retorted shale during the chlorination, The products resulting from the chlorination were in the form of a gaseous metal chloride stream and a solid residue. During the chlorination the residue is reduced to a very fine powder and a large part of this powder is carried along with the volatilized chlorides. Separation of the fine solids from the vapor is readily eflected by passing the solid-gas mixture to a separation zone at temperatures high enough to prevent deposition of the volatilized chlorides on the solid particles. A temperature of 700 C. to about 900 C. should be used in this step. A cyclone separator or an electrostatic precipitator is conveniently used to separate the gaseous stream from the finely divided solids.

We have found that optimum chlorination and vaporization conditions are obtained by bringing the retorted shale into contact with chlorine on a pound for pound basis at temperatures of 600 to 1000" C. Under these conditions, 75 to 95% of the uranium, up to 100% of the iron and up to 90% of the aluminum are volatilized as their respective chlorides. It should be noted that during chlorination of the shale, sulfur chlorides are produced as appreciable amounts of sulfur already exist in the shale.

The vaporized chloride stream is then passed into contact with a molten alkali salt maintained at a temperature in the range 700 to 1000 C. In the case of potassium chloride, for example, the molten salt bed is maintained at a temperature of about 900 to 950 C. and kept at this temperature throughout the period of passing the volatilized chloride stream through the bed. It should be rnoted that for the purposes of our invention, other alkali metal chlorides such as lithium, chlorine and sodium chloride operate in substantially the same manner to quantitatively remove uranium from the vaporized chloride stream.

We have found that the uranium is quantitatively extracted in the molten alkali bath together with reduced quantities of iron and aluminum. Table 2 summarizes the results obtained by passing mixtures of volatilized chlorides of iron, aluminum and uranium through a static volume of a molten alkali chloride. Experimentally prepared volatilized metal chlorides of the other metals present in Chattanooga shale were mixed with volatilized uranium chlorides and streams of chlorides derived directly from retorted shale were also passed through the molten alkali chloride.

The experiments were conducted in an apparatus such as is illustrated in Figure 2. Referring to Figure 2 there is shown a cylindrical column 10 made of Vycor glass for withstanding high temperatures of the order of about 1000" C. or more. The column 10 acts as a container for the molten alkali salt. The-column 10 has an inlet conduit 12 at its upper end for introducing a gas stream. The composition of the gas stream will depend on the particular conditions used as will be described hereinafter. The lower end of the column 10 is extended to form a conduit 14 of smaller diameter than the column 10. The conduit 14 acts as a drain for removing the molten alkali salt.

Column 10 is divided axially into two chambers 11 and 13 by a first porous disc 20. The lower chamber 13 is further delineated by a second porous disc 22 near the bottom of column 10. The lower disc 22 is perforated at its center to receive a tube 24, of Vycor, for example, of approximately half the diameter of column 10. The tube 24 extends upwardly and centrally through the column 10 to the upper porous disc 20. Here the end of tube 24 is flared outwardly and is sealed to the column 10 at the periphery of disc 20. A tubular furnace 28 encloses the upper chamber 11 and two additional tubular furnaces 30 and 32 surround the lower chamber 13. Near the upper end of chamber 13, between furnaces 28 and 30, column 10 is provided with a radial outlet conduit 16 which is sealed to column 10 through a flared connection.

Our experiments were carried out in the abovedescribed apparatus as follows:

A small quantity of an alkali metal chloride, potassium chloride for example, was placed inside the lower chamber 13 of the column 10, which serves as the molten alkali chloride container. A small amount of the salt introduced into the drain 14, melted with a torch and allowed to solidify to form asolid plug seal. The column 10 was then filled with the alkali salt to a point indicated generally at 34, somewhere below the outlet conduit 16. Vycor chips were added as packing to improve the contact of the gas stream with the melt. A mixture of metal chlorides or oxides, depending on the experiment, was placed on top of the upper porous disc 20 in chamber 11. The temperatures in furnaces. 30 and 32 were raised to the exemplary temperature in the ranges shown in Table 2. In the case of potassium chloride for example, the furnaces were raised to a temperature in the range 750 to 950 C. and maintained .at this temperature throughout the entire run. In the case where metal oxides were used, a gaseous stream of dry nitrogen and a chlorinating agent, such as phosgene, was passed over the oxides and the furnace 28 was raised to a temperature in the range 600 to 1000 C. to chlorinate the oxides and to vaporize the resulting chlorides. The volatile chloride stream was then passed down the center tube 24 to cause it to bubble up through the molten alkali bed. The lower porous disc 22 serves as a distributor for the vapor stream. In the case where metal chlorides were used, it was necessary only to vaporize the chlorides and pass them through the center tube 24 and through the molten alkali bed. When the run was completed the potassium chloride plug in conduit 14 was melted with a torch and the contents of the molten bed were drained into a beaker. The resulting cake and any solids which had condensed in the conduit 16 were analyzed to ascertain the distribution of the metal chlorides between the melt and the receiver. The results of a series of such experiments are listed in Table 2.

From the results in Table 2 it is clear that the concentration of uranium relative to iron and aluminum was greatly increased in the molten alkali bath in all cases. Our experiments alsodemonstrated that separation of the uranium from the other metal components of the Chattanoogashale sucha molybdenum, vanadium, titanium and silicon was virtually complete. The complete separation of the uranium from molybdenum and vanadium is especially noteworthy since the latter two elements are notoriously difiicult to remove from uranium.

The deposited uranium may be recovered from the prod vent.

riot mevbe obtained by strieping the sol- In our expen'ments conducted with vaporized retorted "shale chlorides in the apparatus of Figure 2, the chloride TABLE Retention of uranium in molten potassium chloride A purified 5 stream passing from outlet 16 consisted of the chlorides Feed material Temp, 7 Experiment of K01 Weight (grams) Weight ratio bed,

.. Fe .Al V U/ l 5.7 V 22.3 H 0.26 .9.0 26.8 0.34 11.2 12.3 4.5 1.4 18.5 14.2 8.3 1.3 11. 1 15 9.3 8.0 'U' s1 U/Si 22.94 4.34 6.29

U Ti U/Ti "13.9 17.0 0.817 118X10- 57.6' 6.8 2X10- 302X10' 61. 5 6. 2 4X10 214x 68.2 18.1 3X10 In molten sodium chloride Weight (grams) Weight ratio U Fe A1 'U/Fe WA] In molten lithium chloride Weight (grams) Weight ratio r U Fe A1 U/Fe U/Ai Material retained in melt Temp. of K01 Experiment 9e61, Weight (grams) Weight ratio U Fe A] V K U/Fe U/Al U/V WK Si K U/Si WK 0. 04 10. 9 570 2.

Ti K U/Ti U/K 0. 077 11. 7 180. 5 1. 19 E. 6 0. 54 41. 4 20X 10' 217x10 2X10 8. 4 0. 27 47. 3 10- 1,100X10 5. 0 0. 81 18. 0 42X10- 262X10- In molten sodium chloride Weight (grams) Weight ratio U Fe Al N a. U/Fe U/Al U/Na.

In molten lithium chloride Weight (grams) Weight ratio U Fe A1 Li U/Fe U/Al U/Li TABLE 2-Continued Material passed through the melt Temp. of Experiment Ktglaed, Weight (grams) Weight ratio U Fe A1 V K U/Fe U/Al U/V U/K 900-950 0. 003 16 2. 2X10 900-950 0. 22. 5 5. 3 6X10 900-950 0.88 12. 3 4. 5 14. 3 7 X10" 0.2 900-950 0. 21 13. 1 8. 3 11.7 2X10 2X10 900-950 0. 1 15.0 1. 4 900-950 0. 08 7. 7 5. 2 1 X10 U Si K U/Si 900-950 0. 143 4. 31 0. 162 0332 U Ti K U/Tl 900-950 0. 023 16.9 0. 81 00136 750 1X10 52.0 6. 2 44. 2 .025 10 2l l0- 03X10- 850-900 4X10 53. l 5. 9 40. 0 08X10' 75X10- llXlO- 850-900 .034X10' 63.0 17.3 63.7 .034X10' 13Xl0- .034X10 In molten sodium chloride Weight (grams) Weight ratio U Fe Al Na U/Fe U/Al U/N a In molten lithium chloride Weight (grams) Weight ratio U Fe Al Li U/Fe U/Al U/Ll Experiments A through E, L and M were performed by chlorinatlng synthetic mixtures of oxides of the metals indicated Experiments I through K were performed by chlorinating retorted shale.

of iron, aluminum, silicon, titanium, sulfur chlorides and chlorine. This stream is then condensed in a condensation zone at a temperature in the range 100 to 300 C. At these temperatures the chlorides of silicon and titanium as well as sulfur chlorides and chlorine remain volatilized and are removed from the condensation zone. The chlorine and sulfur chlorides may then be separated and recycled to the chlorination zone. The condensed phase now comprises aluminum, ferric and potassium chloride. This condensed phase is vaporized and the resulting chloride stream is passed through a bed of ferric oxide to selectively convert the aluminum chloride to alumina. The alumina thus produced is of good commercial grade and constitutes a valuable by-product of our invention.

The vapor passing from the ferric oxide consists almost entirely of ferric chloride. This ferric chloride is reacted with oxygen at about 1000 C. to form ferric oxide and chlorine. The ferric oxide thus produced is of good commercial grade and constitutes another valuable by-product of our invention. The chlorine may be recycled for use in chlorinating the shale.

We have found that another convenient way of treating the chloride stream from the outlet 16 is to contact the stream with an alkali metal chloride such as potassium chloride at a temperature in the range 500 to 650 C. Iron and aluminum chlorides are selectively retained in the alkali salt. The mass of iron, aluminum and potassium chloride may then be heated in an oxidizing atmosphere to form chlorine and a mixture of ferric oxide and aluminum oxide. The chlorine is recycled for use in chlorinating the shale. The aluminum may be separated from the iron by reacting the mixture of iron and aluminum chloride with sodium hydroxide at elevated temperatures and pressures.

Normally geologic deposits containing such small quantities of uranium as are found in Chattanooga shale would never be considered as potential sources of uranium. However, in accordance with the method of our invention it is now possible to recover the uranium economically and in a substantially pure form. The application of our method of separating uranium has a number of other important advantages. For example, large quantities of aluminum and iron oxides are also produced in accordance with the method of our invention, as applied to Chattanooga shale. Another important advantage is the fact that substantially all of the chlorine is recovered from the volatilized metal chloride stream and may be continuously recycled for use in our process.

While we have described our invention in connection with the problem of recovering and separating uranium from Chattanooga shale, it will be evident that our method is broadly applicable in situations where it is desired to separate uranium from other ores or ore residues containing a high content of aluminum and iron with respect to uranium.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described herein, it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense.

We claim:

1. A method of recovering uranium values from a mixture containing the metals aluminum, iron and uranium comprising heating the mixture with a chlorinating reagent selected from the group consisting of carbon tetrachloride, phosgene, chlorine and a mixture of chlorine and sulfur monochloride to form a stream of vapors of the chlorides of said metals, contacting said chloride stream with a molten alkali metal chloride to quantitatively deposit the uranium therein and extracting the uranium from the alkali metal chloride.

2. The method according to claim 1 wherein the molten 9 alkali chloride is maintained at a temperature in the range 700 to 1000 C.

3. The method according to claim 1 wherein the molten alkali chloride is potassium chloride.

4. The method according to claim 1 where the metal chloride is sodium chloride.

5. The method according to claim 1 wherein the metal chloride is lithium chloride.

6. The process of recovering uranium values from a uranium-bearing ore containing a high ratio by weight of iron and aluminum as compared to that of uranium, comprising heating comminuted ore to remove volatile matter, reacting the heated shal ewith a chlorinating agent selected from the group consisting of carbon tetrachloride, phosgene, chlorine and a mixture of chlorine and sulfur monochloride at a temperature to volatilize uranium chlorides whereby other metal chlorides are also volatilized, contacting the volatilized chlorides with a molten alkali metal chloride to extract the uranium from the vapor and thereafter separating the uranium from said alkali metal chloride.

7. The method according to claim 6 wherein the heated shale is chlorinated at a temperature in the range 600 to 1000" C.

8. The method according to claim 6 wherein the alkali metal chloride is potassium chloride.

9. The process of recovering uranium values from a uranium-bearing ore containing a high ratio by weight of iron and aluminum as compared to that of uranium, comprising roasting comminuted ore, reacting the retorted shale with a chlorinating agent selected from the group consisting of phosgene, carbon tetrachloride, chlorine and mixtures of chlorine and sulfur monochloride at a temperature to vaporize uranium chlorides whereby other metal chlorides are also vaporized, contacting the vaporized chlorides with a molten alkali metal chloride to extract the uranium from the vapor and thereafter separating the uranium from said alkali metal chloride.

10. A method of separating uranium values from a mixture of uranium chloride, aluminum chloride and ferric chloride comprising the steps of heating said mixture to form a volatile stream of said chlorides, and passing said volatilized chlorides into contact with a molten alkali metal chloride to extract the uranium quantitatively and thereafter separating the uranium from said alkali metal chloride.

11. The method according to claim 10 wherein the alkali metal chloride is potassium chloride.

12. A method of recovering uranium values from Chattanooga shale which comprises heating comminuted shale to remove volatile matter, reacting the heated shale with a chlorinating agent selected from the group consisting of carbon tetrachloride, phosgene, chlorine and a mixture of chlorine and sulfur monochloride to form a volatilized metal chloride stream, passing said volatilized chloride 10 stream into contact with a molten alkali metal chloride at a temperature in the range 700 to 1000 C. to deposit the uranium therein and thereafter separating the uranium from said alkali metal chloride.

13. The method according to claim 12 wherein the chlorinating agent is chlorine.

14. The method according to claim 12 wherein the alkali metal chloride is potassium chloride.

15. The method according to claim 12 wherein the alkali metal is sodium chloride.

16. A method of recovering uranium values and other metal values from Chattanooga shale which comprises comminuting the shale, heating the comminuted shale to remove a substantial portion of the organic components in the shale, reacting the heated shale with a chlorinating agent selected from the group consisting of carbon tetrachloride, phosgene, chlorine and a mixture of chlorine and sulfur monochloride to form a volatilized stream of metal chlorides, passing said volatilized stream into contact with a molten alkali metal chloride at a temperature in the range 700 C. to 1000 C. to deposit the uranium therein, contacting the volatile chloride stream passing from said molten alkali metal chloride with solid ferric oxide to convert the aluminum chloride to alumina, reacting the chloride stream passing from said ferric oxide with oxygen to regenerate chlorine and convert ferric chloride to ferric oxide, recycling the thus formed chlorine and separately recovering uranium, iron and aluminum.

17. A method of recovering uranium values and other metal values from Chattanooga shale which comprises comminuting the shale, heating the comminuted shale to remove a substantial portion of the organic components of the shale, reacting the heated shale with a chlorinating agent selected from the group consisting of carbon tetrachloride, phosgene, chlorine and a mixture of chlorine and sulfur monochloride to form a volatile stream of metal chlorides, contacting said volatile chloride stream with a first mass of a molten alkali metal chloride at a temperature in the range 700 to 1000 C. to deposit uranium therein, recovering the uranium from said first molten mass, contacting the chloride stream passing from said first mass with a second mass of an alkali metal chloride at a temperature in the range 500 to 650 C. to remove aluminum and iron, thereafter reacting the second alkali metal chloride mass in an oxidizing atmosphere to convert the iron and aluminum chlorides to their respective oxides and thereafter separately recovering iron and aluminum.

References Cited in the file of this patent UNITED STATES PATENTS 1,434,485 DAdrian Nov. 7, 1922 1,434,486 DAdrian Nov. 7, 1922 1,646,734 Marden Oct. 25, 1927 

1. A METHOD OF RECOVERING URANIUM VALUES FROM MIXTURE CONTAINING THE METALS ALUMINUM, IRON AND URANIUM COMPRISING HEATING THE MIXTURE WITH A CHLORINATING REAGENAT SELECTED FROM THE GROUP CONSISTING OF CARBON TETRACHLORIDE, PHOSGENE, CHLORINE AND A MIXTURE OF CHLOARINE AND SULFUR MONOCHLORIDE TO FORM A STREAM OF VAPORS OF THE CHLORIDES OF SAID METALS, CONTACTING SAID CHLORIDE STREAM WITH A MOLTEN ALKALI METAL CHLORIDE TO QUANTITATIVELY DEPOSITE THE URANIUM THEREIN AND EXTRACTING THE URANIUM FROM THE ALKALI METAL CHLORIDE. 